1. Field of the Invention
The present invention relates to a bag forming, filling, and sealing method that employs a two-ply film, whereby bags are produced from two-ply film in which an internal film and an external film are superposed and filled with product.
2. Description of the Related Art
The use of a two-ply film, in which an internal film and external film are superposed and in which the internal film and external film are sealed in portions (partially sealed) to prevent the occurrence of shifting between the two layers, as a film for use in packaging is known in the art (refer to Japanese Patent Laid-Open Publication No. 20311/97). In such a case, a two-ply bag package material can be fabricated by curving two-ply film into a tubular form and then forming both a vertical seal in the two overlapping edges and an upper horizontal seal and a lower horizontal seal in a direction that intersects the vertical seal portion.
Various techniques for fabricating a package body have been disclosed in a variety of publications in the prior art. For example, bags for “bag-in-box” packaging are disclosed in Japanese Patent Laid-Open Publication No. 2000-185743 and Japanese Patent Laid-Open Publication No. 310296/96. A bag forming, filling, and sealing method that employs film in band form is disclosed in Japanese Patent No. 2553819. Further, bag packages in which a spout is attached on the side surface is described in Japanese Patent Laid-Open Publication No. 2000-190402, and a bag forming, filling, and sealing method that is provided with a cap on the end surface is described in Japanese Patent No. 2775396.
However, the above-described bag forming, filling, and sealing techniques that employ two-ply film have the following problems:
The first problem is the inability to completely eliminate shifting between the two layers of film that occurs in the process of fabricating a two-ply bag package stock. This problem is next described using an example of vertical bag forming, filling, and sealing in which the film moves in a vertical direction.
A two-ply film that has been formed in tubular form by forming a vertical seal portion is caused to move downward by feed rollers on the downstream side. The feed rollers simultaneously grasp the left side and the right side of the cylindrical film between respective pairs of rollers so as to pinch the cylindrical film from the outside on both sides in the horizontal direction. In this case, the outer side of the film is grasped and the inner side of the film does not directly contact the rollers. There is consequently a concern that when rollers are positioned at points that have not undergone partial sealing, the internal film will slip and its relative position consequently shift. This slight shift is held until the position of the next partial seal portion, and if horizontal sealing is carried out in this state, the bag will be sealed with the external film kinked and wrinkled at the horizontally sealed portion. Not only will a seal of this nature naturally be a defective seal, but this type of shift in the film may also result in excessive load on the feed rollers, causing activation of the automatic safety devices and a halt of operation of the packaging machine.
As a second problem, a seal processing step is required in the prior art in which film is paid out from two rolls of stock, superposed, and then sealed to form the two-ply film. This necessity complicates processing and results in higher fabrication costs.
As a third problem, when fabricating packaging stock using two-ply film that is superposed by means of partial seal portions, the occurrence of these partial seal portion in noticeable positions of the packaging material detracts from the appearance of the material. As a solution, the positions where partial seal portions are provided may be vertically or horizontally sealed to conceal the partial seal portions. However, implementing control for aligning the vertical sealing or horizontal sealing with the partial seal portions is complex, and further, discrepancies in the drive timing for vertical seals may result in defective seals.